System and methods for modulating gas input to a gas burner

ABSTRACT

An improved gas appliance having a burner, a gas valve through which the flow of combustion gas to the burner is controlled, and a motor driven blower that supplies combustion air to the burner. The improvement includes means for increasing gas flow through the gas valve as blower speed increases, and decreasing gas flow through the gas valve as blower speed decreases, based on a pressure signal generated independently of combustion air pressure. This improvement allows a constant ratio of gas to air to be maintained in the burner while a combustion flow rate varies dependent on the blower motor revolutions per minute. Thus input pressures of combustion can be controlled at low cost.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/903,484 filed on Jul. 11, 2001, presentlypending, the disclosure of which is incorporated herein by reference inits entirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to gas appliances and,more particularly, to controls for gas input to gas appliances.

BACKGROUND OF THE INVENTION

[0003] Gas appliances typically include valves for controlling gas inputto the appliance's burners. Gas control valves are used in induced draftsystems and in forced draft systems with pressure-assist modulation(PAM) to deliver gas to be combined with air for combustion. It isdesirable to control gas and air input pressures in order to achievedesired combustion rates in appliance burners. One method of controllinggas input pressure is to electronically modulate gas control valveoutput relative to the air input pressure, by using a pressuretransducer. Such an approach, however, is expensive.

SUMMARY OF THE INVENTION

[0004] The present invention in one embodiment is an improved gasappliance having a burner, a gas valve through which the flow ofcombustion gas to the burner is controlled, and a motor driven blowerthat supplies combustion air to the burner. The improvement includesmeans for increasing the flow of gas through the gas valve as the blowerspeed increases, and decreasing the flow of gas through the gas valve asthe blower speed decreases, based on a pressure signal generatedindependently of the combustion air pressure. In a preferred embodiment,a pump provided on the shaft of the blower motor is driven by the blowermotor to generate the pressure signal for controlling the gas valve.

[0005] The above-described system allows a constant ratio of gas to airto be maintained to the burner while a combustion flow rate variesdependent on the blower motor revolutions per minute. Thus inputpressures to the burner can be simply and reliably controlled at lowcost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a schematic diagram of a conventional induced draftcombustion system;

[0007]FIG. 2 is a schematic diagram of a conventional forced draft PAMsystem;

[0008]FIG. 3 is a vertical cross sectional view of a gas valve adaptedfor use with the present invention;

[0009]FIG. 4 is a perspective view of a pump adapted for use with thepresent invention;

[0010]FIG. 5 is a front elevation view of the pump;

[0011]FIG. 6 is a vertical longitudinal cross-sectional view of the pumptaken along the plane of line 6-6 in FIG. 5;

[0012]FIG. 7 is a vertical longitudinal cross-sectional view of the pumptaken along the plane of line 7-7 in FIG. 5;

[0013]FIG. 8 is a side elevation view of the pump;

[0014]FIG. 9 is a bottom plan view of the pump;

[0015]FIG. 10 is a schematic diagram of an induced draft combustionsystem constructed according to the principles of this invention;

[0016]FIG. 11 is a schematic diagram of a forced draft PAM systemconstructed according to the principles of this invention; and

[0017]FIG. 12 is a graph showing pressure generated by the pump as afunction of blower motor revolutions per minute (RPMs).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] A conventional induced draft combustion system is indicatedgenerally as 20 in FIG. 1. The combustion system 20 comprises acombustion chamber 22 having a burner 48 therein, an air inlet 24, and agas inlet 26. A gas valve 100 in the gas inlet 26 controls the flow ofgas to the burner. A blower 30, having an inlet 32 and an outlet 34connected to the combustion chamber 22 draws the hot combustion gasesfrom the combustion chamber to, for example, the heat exchanger of aresidential furnace or commercial heater, thereby drawing air throughthe air inlet 24 into the combustion chamber. In a conventional systemshown in FIG. 1, increasing the speed of the blower 30 increases the airflow to the combustion chamber 22, but it does not affect the flow ofgas to the combustion chamber 22. Thus, changes to the blower speedchange the air to fuel ratio. Additionally, increasing the speed of theblower 30 typically increases air flow to the combustion chamber 22 upto pressures of only about 2.5 inches of water column.

[0019] A conventional forced draft PAM system is indicated generally as40 in FIG. 2. The forced draft system 40 comprises a combustion chamber22 having a burner 48 therein, an air inlet 24, and a gas inlet 26. Agas valve 100 in the gas inlet 26 controls the flow of gas to theburner. A blower 30, having an inlet 32 and an outlet 34 between the airinlet and the combustion chamber 22 pushes air into the combustionchamber, thereby pushing hot combustion gases from the combustionchamber 22 to, for example, the heat exchanger of a residential furnaceor commercial heater. Gas flow is adjusted via a hose line 36 connectingthe blower outlet 34 and a port 110 on the gas valve 100. In theconventional PAM forced draft system shown in FIG. 2, increasing thespeed of the blower 30 increases the air flow to the combustion chamberand affects the flow of gas to the burner. The blower 30, however,produces pressure signals only up to about 2.5 inches of water column.Because gas valves typically operate at pressures above 3 inches ofwater column for natural gas and at pressures above 10 inches of watercolumn for liquefied petroleum (LP) gas, changes to the blower speedcould change the air to fuel ratio when requiring gas valve operation atpressures above 3 inches of water column.

[0020] The present invention is a system and method whereby the fuel gasflow rate is automatically adjusted with changes in the blower speed tosubstantially maintain the air to fuel ratio despite changes in theblower speed. The system includes a gas valve shown generally as 100 inFIG. 3. The gas valve 100 is similar to conventional gas valves, exceptfor the provision of a port for receiving pressure signal from theblower, as described in more detail below. As shown in FIG. 3, the gasvalve 100 comprises a body 101 having an inlet 102, an outlet 104, and aflow path 106 therebetween. There is a main valve 118 adjacent theoutlet 104. The main valve 118 comprises a valve seat 120, and a valvestem 122, which is controlled by a diaphragm 124, and biased closed by aspring 126. The diaphragm 124 defines an upper chamber 128 and a lowerchamber 130 in the valve 100. The relative pressures in the upper andlower chambers 128 and 130 determine the position of the valve stem 122relative to the seat 120, and thus whether the flow path 106 in thevalve 100 is open or closed.

[0021] A control conduit 132, selectively closed by a control valve 134operated by a control solenoid 136, extends to a regulator 138. Apassage 140 has a port 142 opening to the control conduit 132, and aport 144 opening to the lower chamber 130. Thus, when the control valve134 is open, the inlet gas pressure is communicated via conduit 132 andpassage 140 to lower chamber 130, which causes the stem 122 to move andopen the main valve 118.

[0022] The regulator 138 includes a valve seat 146 and a diaphragm 148that seats on and selectively closes the valve seat 146, and whichdivides the regulator into upper and lower chambers 150 and 152. Thereis a spring 154 in the upper chamber 150 on one side of the diaphragm148. The relative pressures in the upper and lower chambers 150 and 152determine the position of the diaphragm 148 relative to the valve seat146, and thus the operation of the regulator 138. A screw adjustmentmechanism 158 compresses the spring 154 and adjusts the operation of theregulator 138. A passage 160 has a port 162 opening to the lower chamber152 of the regulator 138, and a port 164 opening to the upper chamber128 of the valve. When the regulator valve is open, i.e. when thediaphragm 148 is not seated on valve seat 146, the inlet gas pressure iscommunicated via passage 160 to the upper chamber 128, tending toequalize the pressure between the upper and lower chambers 128 and 130,and close the main valve 118.

[0023] A secondary valve 166, comprising a valve seat 168, a valvemember 170, and solenoid 136, is disposed in the flow path 106 betweenthe inlet 102 and the main valve 118. The secondary valve 166 alsocloses the gas valve 100, acting as a back up to the main valve 118.

[0024] In accordance with this preferred embodiment, the regulator 138includes a port 174 that communicates with the upper chamber 150 forreceiving a pressure signal from a blower-driven pump as furtherdescribed below. The pressure signal on the port 174 changes theoperating point of the regulator. When the pressure signal from port 174increases the pressure in the upper chamber 150 of the regulator, theregulator valve closes passage 160, tending to increase the opening ofthe main valve 118. When the pressure signal from the port 174 decreasesthe pressure in the upper chamber 150 of the regulator, the regulatorvalve closes less readily, keeping passage 160 open, and tending toclose the main valve. Thus the port 174 provides feed back control,increasing gas flow with an increase in blower speed, and decreasing gasflow with a decrease in blower speed.

[0025] In accordance with this invention, the pressure signal ispreferably created by the operation of the blower motor. In thepreferred embodiment, a pump is provided on the shaft of the blowermotor. Rotation of the blower motor shaft operates the pump, and theoutlet pressure of the pump is substantially proportional to the speedof the blower motor.

[0026] A pump adapted for use with the present invention is indicatedgenerally as 200 in FIGS. 4 through 9. The pump 200 comprises a housing202 having a one-way air inlet 204 and an air outlet 206. A diaphragm208 in the housing 202 is operated by the reciprocation of a shaft 210,which in turn is driven by cam 212. The cam 212 is operatively connectedto shaft of the blower motor. The pump 200 has a socket 214 for engagingthe shaft of the blower motor. Thus the pressure generated by the pumpchanges with the speed of the blower motor.

[0027] An induced draft combustion system constructed according to theprinciples of this invention is indicated generally as 300 in FIG. 10.The combustion system 300 is similar in construction to system 20described above, and corresponding parts are identified withcorresponding reference numerals. The combustion system 300 comprises acombustion chamber 22 having a burner 48 therein, an air inlet 24, and agas inlet 26. A gas valve 100 in the gas inlet 26 controls the flow ofgas to the burner 48. A blower 30 connected to the combustion chamberdraws the hot combustion gases from the combustion chamber 22 to, forexample, the heat exchanger of a residential furnace or commercialheater, thereby drawing air through the air inlet 24 into the combustionchamber.

[0028] In system 300, a pump 200 is mounted on the shaft of the motor ofthe blower 30. The outlet 206 (shown in FIGS. 4-9) of the pump 200 isconnected to the port 174 in gas valve 100 via line 302, to adjust theoperation of the regulator with changes in the blower speed, therebytending to maintain the air to fuel ratio as the blower speed changes.The pump outlet pressure is generated independently of, and can exceed,the combustion air pressure generated by the blower 30. Thus anadjustable bleed orifice 310 of the line 302 is used to adjust the pumppressure signal to the gas valve 100. Thus the pump 200, line 302,orifice 310 and port 174 operate as a controller that increases the flowof gas through the gas valve 100 as the blower speed increases, anddecreases the flow of gas through the gas valve 100 as the blower speeddecreases, based on a pressure signal substantially proportional todrive shaft revolutions of the blower motor.

[0029] A differential pressure switch 320 between the air inlet 24 andgas valve outlet 104 is configured to sense both gas flow and air flowinto the combustion chamber 22. When a predetermined difference in gasflow and air flow is sensed, the switch 320 cooperates, for example,with a system 300 ignition or blower motor control (not shown) to shutdown the system 300. Thus an automatic shutoff is performed if, forexample, lint accumulates in the air inlet 24 in such amounts that thepredetermined difference in gas and air pressures is detected.

[0030] A PAM combustion system constructed according to the principlesof this invention is indicated generally as 400 in FIG. 11. Thecombustion system 400 is similar in construct to system 40, describedabove, and corresponding parts are identified with correspondingreference numerals. The combustion system 400 comprises a combustionchamber 22 having a burner 48 therein, an air inlet 24, and a gas inlet26. A gas valve 100 in the gas inlet 26 controls the flow of gas to theburner 48. A blower 30 between the air inlet and the combustion chamberpushes air into the combustion chamber, thereby pushing hot combustiongases from the combustion chamber 22 to, for example, the heat exchangerof a residential furnace or commercial heater. In system 400, a pump 200is mounted on the shaft of the motor of the blower 30. The outlet 206(shown in FIGS. 4-9) of the pump 200 is connected to the port 174 in gasvalve 100 via a line 402, to adjust the operation of the regulator withchanges in the blower speed, thereby tending to maintain the air to fuelratio as the blower speed changes. The pump outlet pressure is generatedindependently of, and can exceed, the combustion air pressure generatedby the blower 30. Thus an adjustable bleed orifice 410 of the line 402is used to adjust the pump pressure signal to the gas valve 100. Thusthe pump 200, line 402, orifice 410 and port 174 operate as a controllerthat increases the flow of gas through the gas valve 100 as the blowerspeed increases, and decreases the flow of gas through the gas valve 100as the blower speed decreases, based on a pressure signal substantiallyproportional to drive shaft revolutions of the blower motor.

[0031] A differential pressure switch 420 between the blower outlet 34and gas valve outlet 104 is configured to sense both gas flow and airflow into the combustion chamber 22. When a predetermined difference ingas flow and air flow is sensed, the switch 420 cooperates, for example,with a system 400 ignition or blower motor control (not shown) to shutdown the system 400.

[0032]FIG. 12 is a graph showing pressure generated by the pump 200 as afunction of blower motor RPMs. It can be seen that the relationshipbetween inches of pump outlet pressure and RPMs of the blower motor issubstantially linear, and that the pump 200 is capable of generatingpressures exceeding typical blower generated combustion air pressures ofup to 2.5 inches of water column.

[0033] The above system and method provide for maintaining a constantratio of gas to air going to a furnace while varying a combustion flowrate dependent on blower motor revolutions per minute. Because the pump200 generates a pressure signal dependent on the blower motor speed, gasflow can be modulated without sensing or sampling combustion airpressure. The pump can be configured with gas valves that operate atpressures above, below and including two inches of water column. Morespecifically, the pump can provide pressures of up to fourteen inches ofwater column. Thus the pump produces pressures sufficient for use in gasappliances having burners using either natural or LP gas, and also isinexpensive to manufacture. Thus input pressures of combustion can becontrolled at low cost.

[0034] Other changes and modifications may be made to the abovedescribed embodiments without departing from the scope of the presentinvention, as recognized by those skilled in the art. Thus the inventionis to be limited only by the scope of the following claims and theirequivalents.

What is claimed is:
 1. An improved gas appliance having a burner, a gasvalve through which the flow of combustion gas to the burner iscontrolled, and a motor driven blower which supplies combustion air tothe burner, the improvement comprising means for increasing the flow ofgas through the gas valve as the blower speed increases, and decreasingthe flow of gas through the gas valve as the blower speed decreases,based on a pressure signal generated independently of the combustion airpressure.
 2. The improved gas appliance according to claim 1 wherein thepressure signal is generated dependent on the blower motor speed.
 3. Animproved gas appliance having a burner, a gas valve through which theflow of combustion gas to the burner is controlled, and a motor drivenblower which supplies combustion air to the burner, the improvementcomprising a controller configured to increase the flow of gas throughthe gas valve as the blower speed increases, and decrease the flow ofgas through the gas valve as the blower speed decreases, based on apressure signal having pressure capable of exceeding the combustion airpressure.
 4. The improved gas appliance according to claim 3 wherein thegas valve decreases the flow rate as the pressure signal increases, andincreases the flow rate as the pressure signal increases.
 5. Theimproved gas appliance according to claim 3 wherein the controllercomprises a pump for providing the pressure signal to the gas valve. 6.The improved gas appliance according to claim 5 wherein the pump isdriven by the blower motor.
 7. The improved gas appliance according toclaim 3 wherein the controller further comprises an adjustable bleedorifice configured to adjust the pressure signal relative to the gasflow.
 8. The improved gas appliance according to claim 3 wherein theblower pushes air into the burner.
 9. The improved gas applianceaccording to claim 3 wherein the blower draws air through the burner.10. The improved gas appliance according to claim 3 wherein thecontroller further comprises a differential pressure switch configuredto deactivate the appliance based on a predetermined pressure differencebetween gas flow and air flow into the burner.
 11. A gas combustionsystem comprising a burner, a gas valve for controlling the flow of gasto the burner, a motor-driven blower that provides combustion air to theburner, and a controller for controlling the flow of gas through the gasvalve responsive substantially proportionately to the blower motorspeed, increasing the flow of gas as the blower speed increases anddecreasing the flow of gas as the blower speed decreases.
 12. The gascombustion system according to claim 11 wherein the gas valve has aregulator for controlling the flow of gas through the gas valve, and aport for receiving a pressure signal for operating the regulator tocontrol the flow of gas through the gas valve, and wherein thecontroller provides a pressure signal to the port.
 13. The gascombustion system according to claim 12 wherein the controller comprisesa pump for providing a pressure signal to the port.
 14. The gascombustion system according to claim 13 wherein the pump is driven bythe blower motor.
 15. The gas combustion system according to claim 13wherein the regulator decreases the flow rate as the pressure signal atthe port decreases, and increases the flow rate as the pressure signalat the port increases.
 16. The gas combustion system according to claim12 wherein the regulator decreases the flow rate as the pressure signalat the port decreases, and increases the flow rate as the pressuresignal at the port increases.
 17. The gas combustion system according toclaim 12 wherein the blower pushes air into the burner.
 18. The gascombustion system according to claim 13 wherein the blower draws airthrough the burner.
 19. A gas combustion system comprising a burner, acombustion gas inlet for providing combustion gas to the burner, a gasvalve in the gas inlet for controlling the flow of gas through the gasinlet at least partly in response to a pressure signal, a motor-drivenblower for providing combustion air to the burner, and a pump forproviding a pressure signal to the gas valve for controlling the flow ofgas to the burner, said pump being responsive to the blower motor speed,increasing the flow of gas as the blower motor speed increases anddecreasing the flow of gas as the blower motor speed decreases.
 20. Thegas combustion system according to claim 19 wherein the blower pushesair into the burner.
 21. The gas combustion system according to claim 19wherein the blower draws air through the burner.
 22. The gas combustionsystem according to claim 19 wherein the combustion air to combustiongas ratio remains substantially constant with changes in the blowerspeed.
 23. The gas combustion system according to claim 19 furthercomprising an adjustable bleed orifice configured to adjust the pressuresignal to the gas valve.
 24. The gas combustion system according toclaim 19 further comprising a differential pressure switch configured todeactivate the gas burner system based on a pressure difference betweengas flow and air flow into the burner.
 25. In combination with a gasappliance having a burner, a gas valve through which the flow of gas tothe burner is controlled based on a pressure signal, a motor-drivenblower for providing combustion air to the burner, and a controller forcontrolling the flow of gas through the gas valve, a pump configured toprovide a pressure signal to the controller dependent on blower motorspeed, said pump further configurable to provide pressure signalssufficient to operate appliances utilizing a plurality of types of gas.26. The combination according to claim 25 wherein the pump is configuredto maintain a substantially constant gas-to-air ratio going to theappliance burner.
 27. The combination according to claim 26 wherein thepump is configured to provide a pressure signal of up to about fourteeninches of water column to the controller.
 28. A method for controllingthe flow of gas to the burner of a gas combustion system, the combustionsystem including a gas valve through which the flow of gas to the burneris controlled and a motor-driven blower for providing combustion air tothe burner, said method comprising the steps of: converting revolutionsof a drive shaft of the blower motor into a pressure signalsubstantially proportional to the speed of the blower motor; andcontrolling gas flow to the burner based on the pressure signal.
 29. Themethod according to claim 28 wherein said steps are performed withoutsensing or sampling the combustion air pressure.
 30. The methodaccording to claim 28 wherein the step of controlling gas flow comprisesadjusting the pressure signal relative to the gas flow using anadjustable bleed orifice.